1. Field of the Invention
The present invention relates to optically active compounds useful for display devices or electrooptical devices, ferroelectric smectic liquid crystal compositions containing them and ferroelectric smectic liquid crystal display devices.
2. Discussion of the Background
Liquid crystal devices using nematic liquid crystals, which used to be employed for the display portions of watches, electric calculators, etc., have a response speed substantially lower than other display devices such as a light emission diode. Therefore, their application to the fields where a quick response is required, such as to liquid crystal display devices for optical communication systems or printer heads, has been limited.
Recently, liquid crystal display devices using smectic liquid crystals showing ferroelectricity have been reported as liquid crystal display devices showing a quick response (for example, N. A. Clark, S. T. Lagerwall, Appl. Phys. Lett. 36, 899 (1980)).
The ferroelectric smectic liquid crystals include a chiral smectic C-phase and a chiral smectic H-phase. They show a layered structure in which liquid crystal molecules are not perpendicular but inclined to the lamination direction of the layers. The direction of this inclination is such that the liquid crystal molecules are arranged in a spiral form relative to the direction of the lamination of the layers, whereby a spontaneous polarization is created in a direction parallel to these layers and perpendicular to the liquid crystal molecules, thus showing ferroelectricity. This spiral structure is believed to be attributable to the ferroelectricity. A ferroelectric material exhibits a response to an electric field, as a ferroelectric substance. Namely, the direction of the spontaneous polarization will be inverted and the liquid crystal molecules will be rearranged depending upon the direction of the electric field.
It is known that the greater the spontaneous polarization and the lower the viscosity, the quicker the response to the same strength of the electric field. Further, a device using such ferroelectric smectic liquid crystals has a memory property, and researches are being actively conducted to develop a high density display system utilizing this memory property.
Heretofore, various researches have been made on the following Schiff base type compound as a ferroelectric smectic liquid crystal: ##STR5## p-Decyloxybenzylidene-p'-amino-2-methylbutylcinnamic acid ester (DOBAMBC)
However, such a Schiff base type compound is susceptible to hydrolysis, and thus has a problem that it is likely to be decomposed by moisture.
Further, compounds represented by the following formula II have been known as ester-type compounds showing a chiral smectic C-phase (G. W. Gray et al., Mol. Cryst. Liq. Cryst., 1976, 37 189-211). ##STR6## where R is a straight chain alkyl group having from 5 to 10 carbon atoms.
However, these ester compounds have a difficulty that their spontaneous polarization is low although they are resistant to moisture.
Recently, a compound having the following formula and referred to as "DOBA-1-MBC" has been reported as a compound having a high spontaneous polarization (K. YOSHINO et al., J.J.A.P., 1984 23, L, 175-177). ##STR7## However, this compound is also a Schiff base type and accordingly has a drawback that it is likely to be decomposed by moisture.